What Microchip doesn't (officially) tell you about the VSC8512

Summary

Switch project, part 3 - what Microchip doesn't (officially) tell you about the VSC8512 2025-07-04 08:00 This is part 3 of my ongoing series about LATENTRED, my project to create an open source 1U managed Ethernet switch from scratch. Here’s a quick, or maybe not-so-quick, update about the PHY on the line card and some of my troubles (and solutions). And probably more internal details than you want to know, but hey - maybe this will be useful to somebody. Not a lot of pretty pictures either. One day I do want to decap one for fun, but I have better things to do with my time than try to fully netlist-extract a large 65nm IC just to figure out some undocumented registers. Background I chose the VSC8512 as the PHY for the line card because it had a QSGMII interface (which used much less pins than SGMII), but also (so I thought) had a fully open datasheet with no NDAs required. Typically I’m used to seeing parts that are either fully NDA’d (with a trivial product brief and no register info etc, or sometimes not even pinout info, public), or fully open. Sometimes I find components with specific documents restricted, but it’s almost always clear that “this document/ref design exists, you can’t get it without an NDA, but we are openly telling you we’re holding it back”. In my previous post I mentioned that there was no documentation for how to change the SERDES TX equalizer settings on the PHY side of the QSGMII. I opened a support case and Microchip responded saying that additional info was available in the “confidential reference manual” for the part which required an NDA. The rest of the reply was pretty generic and mentioned indirect register access but no specifics. I was quite annoyed at this, as I had specifically chosen the part believing there was no restricted documentation. Since signing an NDA wasn’t an option, it seemed I had the choice of suboptimal signal integrity or figuring things out from the limited public information. The eye was still reasonably open ...